With U.S. advisers and firepower, Syrian forces aim to sever the Islamic State's last escape route from Raqqa

WASHINGTON — U.S. military advisers, aircraft and artillery are helping Syrian fighters secure a strategic dam outside the Islamic State's capital of Raqqa, where they're battling to cut off the militants' only remaining escape route, officials said.

Officials did not specify how many U.S. advisers are on the ground as part of the operation to retake the Tabqa dam, where the U.S. military has transported more than 500 Syrian fighters for the operation, which was launched on Tuesday.

U.S. Army Apache helicopters and Marine artillery are also supporting the ongoing operations, officials said.In recent weeks, the Marines have moved several M777A2 Howitzers to a fire base near Raqqa.

The operation to retake the Tabqa dam is intended to "reclaim the last route in and out of Raqqa," said Pentagon spokesman Eric Pahon. He declined to provide further details.

Members of the U.S.-backed Syrian Democratic Forces, one of the groups Washington is supporting in its counter-ISIS fight, have said the ground force includes several U.S. Marines, reportedly shuttled into ISIS-held territory to help retake four villages while severing the main route extending from Raqqa to the western countryside.

Local Syrian forces were inserted just to the south of the Tabqa dam with the aid of U.S. helicopters, said Col. Joe Scrocca, a spokesperson for Operation Inherent Resolve. The air assault operation was described as an "initiative" by the Syrian Democratic Forces with U.S. forces in a supporting role, according Joe Scrocca said on Wednesday."First time we have conducted such an operation."

"It takes a special breed of warrior to pull of an airborne operation or air assault behind enemy lines," Scrocca said.

The operation to take back the dam, held since 2013 by ISIS fighters, could take several more weeks because forces have to secure an airfield, a small town, and the dam itself, he explained.

U.S. forces are supporting a variety of Syrian forces focused on defeating ISIS. They Syrian Arab Coalition is composed of Arab fighters mixed with elements of the Syrian Democratic Forces and some Kurdish factions. The group issued a statement on social media Wednesday indicating the dam operation comes in preparation for an assault on Tabqa, some 28 miles west of Raqqa.

US artillery unit joined the clashes between SDF and Daesh around Karama town East Raqqa

An activist group indicated 500 U.S. and Syrian Kurdish forces were deployed for the operation to retake the dam. The group relies on local contacts to smuggle information out of ISIS territory.

A pro-Kurdish website also tweeted on Wednesday that U.S. artillery is supporting friendly forces focused on Raqqa. An unconfirmed video posted Wednesday shows a U.S. High Mobility Artillery Rocket System targeting ISIS, purportedly from a base near Kobani however, U.S. officials could only confirm that HIMARS were in support of the operation, but did not know if any rockets had actually been fired.

Shawn Snow is a Military Times staff writer and Early Bird Brief editor. On Twitter: @SnowSox184

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The Associated Press and

Marine Corps Times reporter Jeff Schogol contributed to this story. On Twitter: @JeffSchogol

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